Supernatants from activated lymphocytes contain lymphokines which can exert growth-inhibitory and cytolytic effects on cells in vitro. Important members of these lymphokines are lymphotoxins (LTs). Serological evidence supports the role of some LTs in cell-mediated cytotoxic reactions in vitro. Furthermore, selective tumoricidal and anticarcinogenic effects in vitro have been ascribed to LTs. The present project will undertake the following: (1)\biochemical characterization of homogeneous human alphaL LT from lectin-activated normal lymphocytes; (2)\documentation of homogeneity and biochemical characterization of alphaH LT from lectin-stimulated normal lymphocytes; (3)\continued development and characterization of antisera and monoclonal antibodies specific for alphaL and alphaH LT; (4)\in collaboration with Biogen, cloning of the gene from RPMI-1788 B-lymphoblastoid line coding for alphaL in yeast; (5)\development of specific, cytotoxic human T-killer lines and T-T hybridomas, and isolation and characterization of receptor-bearing, cytotoxic molecules therefrom; (6)\testing of homogeneous alphaL and alphaH LT and recombinant alphaL for selective tumoricidal effects and ability to colony-inhibit chemical carcinogen-transformed fibroblasts in vitro; (7)\blocking of cell-mediated cytotoxic reactions in vitro with immunological reagents specific for alphaL and alphaH LT; and (8)\use of cDNA probes from (4) to isolate mRNA from cytotoxic T-cell lines and T-T hybridomas. (HF)